I hope Slat doesn't mind me giving my answers/opinions on some of these.
One suggestion I will give you question askers is to refer to the level/league/whatever you are asking the question about. Answers (not just on rules, but game management) could be vary different depending on the league/level.
How often do refs talk to each other about missed/bad calls or tightening/loosening things up depending on game flow?
As far as missed/bad calls, it depends on who I am reffing with. It it's a friend or someone I feel comfortable bringing it up on my own, I will. If it's someone that I don't know at all or think they will take offence to me bringing it up, I will keep it to myself. If my partner (or ref while I'm lining) asks me, I will give my honest opinion and talk about the call with them.
Is there typically a senior ref assigned and if not is it common for a one of the refs to assume a seniority role?
There are some games I get assigned and I know it's for the purpose of being the more experienced of the 2 of us. For most games, my partner and I are equals. I always show a lot of respect for the more seniors (in age or experience) guys and ask them about calls to see their opinion. I'm not afraid to ask their opinion about calls I've made but I think a lot of refs don't think the same way.
We had a game the other night where one of the refs had only 1 game under his belt and it showed. Whistle in the pocket and major indecisiveness when it wasn't. We were chirping the other ref because we've known him for a while and he's a pretty good ref but he he wouldn't respond at all when we were asking if he'd talk to the other guy.
The only real thing that pissed us off was a major slew foot behind the play but right in front of him he watched the whole time. Nearly ended up in a brawl.
As I stated above, the level of this game could change my answer big time. If he only had 1 game ever previously, I'm hoping this was a adult league game. If I was the other ref in this situation, I will give my partner pointers and bring up a few missed/bad calls. To reply to the players, I would state his experience level, ask you to cut him some slack, and talk to him about the questionable calls you brought up and (I assume) I did not see.